PHP include warnings -

i have 2 php-files.

source/dao/winkelwagendao.php

here i:

include_once($_server['document_root'].'/itbee/model/winkelwagenitem.php'); 

then have: source/model/winkelwagenitem.php -> getters , setters

now on onchange event in jquery ajax-request winkelwagendao file, catch request in dao file , call appropriate function -> updateaantal()

catch:

if(isset($_post['function'])) {     $action = $_post['function'];      switch ($action) {         case 'updateaantal' :             echo "\naan te passen aantal voor productid: " . $_post['productid'] . " gebruik functie: " . $_post['function'] . " set aantal naar: " . $_post['aantal'];             winkelwagendao::updateaantal($_post['productid']);     } } 

updateaantal() function:

public static function updateaantal($productid) {          if (isset($_cookie["winkelwagen"])) { //cookie exists?             $array = self::getwinkelwagenitems();              $index = 0; //positie bijhouden              foreach ($array $product) {                 if ($productid == $array[$index]->getproductid()) {                     //echo $productid . " == " . $array[$index]->getproductid();                      $array[$index]->setaantal($_post['aantal']);                     $serializearray = serialize($array);                     setcookie("winkelwagen", $serializearray);                      break; //quit if match                 } else {                     $index++;                 }             }         } else {             echo "this cookie did not exist";         }     } 

seems can not access getters winkelwagenitem php class because include_once not working correctly. although think path correct? reason why use $_server['document_root'].

when error in console , 2 warnings:

warning: include_once(./dao/productdao.php): failed open stream: no such file or directory in /applications/mamp/htdocs/itbee/model/winkelwagenitem.php on line 2

warning: include_once(): failed opening './dao/productdao.php' inclusion (include_path='.:/applications/mamp/bin/php/php5.6.6/lib/php') in /applications/mamp/htdocs/itbee/model/winkelwagenitem.php on line 2

warning: cannot modify header information - headers sent (output started @ /applications/mamp/htdocs/itbee/model/winkelwagenitem.php:2) in /applications/mamp/htdocs/itbee/dao/winkelwagendao.php on line 137

the warnings failed include second line of /itbee/model/winkelwagenitem.php file. include tries find ./dao/productdao.php file, doesn't exist. should search in winkelwagenitem.php solve issue. didn't post code here.
remarks of question irrelevant problem.